Method of operating retort gas plan&#39;ts



May 15, 1934. s. P.-M|LLER METHOD OF OPERATING RETORT GAS PLANTS fi M INVENTOR AT TORNEYS May 15, 1934. I s. P. MILLER METHOD OF OPERATING RETORT GAS PLANTS Original Filed April 18, 1928 3 Sheets-Sheet J F M INVENTOR ATTORNEYS May 15, 1.934. s. P. MILLER METHQD 0F OPERATING RETORT GAS PLANTS 1928 3 Sheets-Sheet 3 Original Filed April 18 INVENTOR AT TORNEY5 UNITED STATES 1,959,289 PATENT OFFICE METHOD OF OPERATENG RETORT GAS- PLANTS Stuart Par-melee Miller, Scarsdale, N. Y assignor to The Barrett Company, New York, N. Y., a corporation of New Jersey Application April 18, 1928, Serial No. 271,064 Renewed January 27, 1934- Claims". (01. 202-) This invention relates to improvements in the operation of retort gas plants in which coal is distilled for the production of coal gas. The invention includes improvements in the distillation of tar at such plants and the production of pitches and oils therefrom. The invention also includes improvements in the operation of such plants, and particularly in the operation of the standpipes of such plants.

In horizontal and inclined retort coal gas plants, the gases from the individual retorts are delivered to the hydraulic main or other collect-- ing mains through vertical standpipes. In some plants each individual retort is provided with its own standpipe. In other plants one standpipe serves to deliver the gases from all the retorts of one tier or even from two or more tiers of retorts to the hydraulic or gas collecting main. The gases leave the retorts at a high temperature, for example, around 500 C. to 800 C. but in passing through the standpipes tothe hydraulic or gas collecting main they are rapidly cooled, for example, to temperatures around 200 C. to 250 C. As a result, a considerable amount of the tar contained in the gases is condensed on the cooled Walls of the standpipes and this tar tends to flow down and to be distilled by contact with the hot gases, leaving a residue of pitch and carbon or coke on the Walls of the standpipe so that frequent cleaning is required to prevent clogging of the standpipe.

It has heretofore been proposed to prevent the accumulation of pitch and carbon on the standpipe Walls and to cool the gases rapidly in the standpipes by the circulation of water, etc. in-

side the standpipes, the water entering the top of the standpipes, for example, at a temperature around C. and leaving the bottom of the standpipes together with tar at a temperature around 50 C. The use of water for this purpose is claimed to keep the standpipes clean from pitch and carbon accumulation and to cool the gases and separate most of the tar therefrom so that the burden on the condensing system of the plant and on the rest of the apparatus is reduced.

The tar separated from the cooled gases in the standpipes is collected with the water at the bottom of the standpipes, the tar separated from the Water, and the water recirculated. The tar so collected is commonly shipped to tar distillation plants and there distilled, frequently in admixture with other tars; particularly coke oven tar.

The present invention provides an improved method of operation of retort gas plants in which the objectionable accumulation of pitch and carbon in the standpipes is prevented or minimized without the rapid cooling of the gases to separate tar therefrom, and with utilization of the heat of the gases in the standpipes for the distillation of tar and the production of pitch and distillate oils therefrom.

According to the present invention, the gases from the retorts passing through the standpipes are prevented from being rapidly cooled, and are kept at a sufilciently high temperature to enable them to be utilized eifectively for the distillation of tar, and tar to be distilled is brought into intimate contact therewith to effect its distillation and the production therefrom of a pitch residue and of distillate oils which escape from the standpipes with the gases. The present invention enables the tar produced at a retort gas plant to be distilled at such plant, either by itself or in admixture With other tar, such as coke oven tar, so that merchantable pitch products can be directly produced at the retort gas plant, as well as distillate oils. The invention also includes improvements in the operation of such retort gas plants, and particularlyin the operation of the standpipes of such plants, whereby the gases from the retorts are kept at a high temperature and employed for distillation of tar in said standpipes, and in which the resulting gases, enriched in oil vapors from the distillation, are drawn off and subjected to condensation to recover distillate oils together with oil constituents present in the gases resulting from the distillation.

In retort gas plants having individual standpipes for individual retorts, particularly horizontal and inclined retorts, the charges of coal subjected to distillation are relatively small, and the volume of gases produced per retort charge is relatively small. However, in retort plants having multiple standpipes, in which a single standpipe is connected to several retorts, a much greater volume of gases passes through the individual standpipe, and, where the retorts are charged at difierent times, a continuous flow of gases is produced which, with several retorts connected to the same standpipe, approximates a uniform flow of gases. Such plants, having multiple standpipes, can advantageously be utilized for the practice of the invention.

In carrying out the invention, the gases from the individual retorts are prevented from being suddenly cooled to a low temperature, and are maintained at a high temperature, which may approximate the highest practicable temperature, that is, a temperature not greatly below that at which the gases leave the retorts. This preven-1 tion of sudden cooling can be effected by applying heavy insulation to the standpipes. The high temperature gases are thus maintained at a high temperature in the standpipes and are brought into intimate contact with the tar to be distilled so that effective distillation will take place.

The tar to be distilled is introduced directly into the standpipes and there brought into intimate contact with the hot gases passing therethrough. The tar is introduced in sufiicient amount and in such a regulated manner as to keep the walls of the standpipes clean from objectionable pitch and carbon deposits. It is also introduced in such a manner as to bring it into intimate contact with the hot gases passing through the standpipes. Tar spread out over the walls of the standpipes and flowing downwardly thereover has a large surface exposed in the form of a continuous film for contact with the hot gases. The contact can be promoted by atomizing or spraying the tar into the standpipes and causing it to flow downwardly therethrough in a finely subdivided form in opposition to the upwardly rising current of hot gases. A sufiicient amount of tar will be introduced to insure that there will be a sufiicient amount of pitch residue flowing from the bottom of the standpipes to keep the walls clean from pitch and carbon accumulations and to give a pitch product which can be handled. A considerable excess of tar can be introduced and only partial distillation effected, and the resulting pitch then recirculated and subjected'to further distillation, either in the same or in different standpipes, and either with or without the addition of further amounts of tar.

The utilization of the hot gases for tar distillation, particularly where the tar is sprayed or atomized into the gases, results in a scrubbing of the gases and the removal therefrom of a greater or less part of the suspended carbon and pitch particles which are added to the tar and pitch flowing downwardly through the standpipes and collected as part of the pitch residue. The distillation also increases the content of vapors carried by the gases so that the gases are both cleaned and enriched in oil vapors. These enriched gases can then be subjected to cooling to condense the distillate oils and other oil and tar constituents carried thereby to produce oil products of a merchantable character.

Depending on the rate at which the tar is supplied, the temperature and volume of the gas, the intimacy of contact of the tar and gases, etc. the gases may leave the standpipes enriched in oil vapors at a high temperature, e. g. in excess of 1.50 or 200 C. or in some cases up to 250 or 27.5" C. or higher, and may contain high boiling oil and resin constituents which are valuable for creosoting and other purposes.

The pitch residue drawn off from the bottom of the standpipes can be regulated so as to produce pitches of higher or lower melting points. If sufficient distillation is not effected by passing the tar once through the standpipes and distilling it during such passage to produce pitch, the resulting low melting point pitch can be recirculated and further distilled, either in the same standpipe or in another standpipe or standpipes, to produce pitch of higher melting'point. In such case, instead of introducing tar into the top of the standpipes, a partially distilled tar or partially distilled pitch can be so introduced and further distilled to produce a pitch of higher melting point.

The gases coming off from the standpipes, after the distillation of tar or pitch therewith, need not be cooled in a hydraulic main but may be passed directly to a foul gas main or to a condensing system. If they still contain too large a content of heavy pitch constituents so that the oil is a tarry oil, they can be subjected to further treatment to remove heavy pitch constituents therefrom. They can, for example, be subjected to cleaning with an electrical precipitator at a sufflciently high temperature to take out pitch particles therefrom while still leaving a large proportion of the oils in the form of vapors, and the gases can then be cooled to condense clean oils therefrom, for example, clean creosote oils, or clean tar acid oils, etc. The gases can also be further cleaned at a high temperature by scrubbing in a pitch scrubber and heavy pitch particles removed therefrom, leaving clean or relatively clean gases from which clean or relatively clean oils can be condensed and directly recovered. The partial scrubbing or cleaning of the gases in the standpipes, and the enrichment of the gases in oil vapors, will give a tarry oil with much'less than the normal heavy tar and pitch constituents, even though the gases are not subjected to further cleaning treatment before cooling and condensation of oils therefrom.

The tar which is subjected to distillation, ac-

cording to the present invention, may be that produced at the retort gas plant at which the distillation is carried out. In such cases, a part only of the plant will be required for the distillation of the tar, and the tar may be collected and condensed from the remainder of the plant in the usual way. Where additional tar is available, as where several retort gas plants are so located that their total tar production can be handled together, one plant may be employed as a whole for tar distillation, and the other plants operated in the ordinary way with separation and collection of tar from the coal distillation gases.

The tar produced in gas retort plants of the character under discussion is commonly blended by the tar distiller with other tar or tars, for example, coke oven tars, and the blended tars are then distilled. This practice has resulted from the fact that retort gas tar, particularly from horizontal and inclined retort gas plants, is ordinarily much richer in free carbon than is coke oven tar, and the pitches produced by distillation of gas retort tar likewise contain much more free carbon than do the pitches of corresponding melting point derived from coke oven or other tars. The content of free carbon contained in coal tar pitch governs to a considerable degree the char-- acter of the pitch and largely determines its utility in numerous applications to which coal tar pitches are put. Many pitches are sold under specifications requiring definite minimum percentages of free carbon and can be made only from tars of high free carbon content, higher than ordinary coke oven tars. It is customary, therefore, for tar distillers to blend high carbon gashouse tars with lower carbon coke oven tars to the extent necessary to insure the required free carbon content in the pitch resulting from the distillation. Coke oven tars Vary, for example, in free carbon content from around 2.5% to around 8%, while gas-house tars vary in carbon content 1 from around 6% to around 35%.

The present invention is a particularly advantageous one for producing composite pitch products of regulated carbon content by employing lower carbon tars and subjecting them to distillation according to the invention. The lower carbon content of coke oven tars makes them more valuable for flushing the walls of the standpipes and preventing pitch and carbon accumulations thereon. Coke oven tars can be employed withof carbon and pitch constituents from the gases during the distillation results in an increase in carbon content of the pitch produced, even where low carbon coke oven tars are employed in the standpipes for flushing the standpipes and for distillation by the hot retort gases. That is, the pitch scrubbed from the gases will be higher in carbon content than that resulting from the distillation of the coke oven tar, and the resulting composite pitch will therefore be a higher carbon pitch than it would otherwise be. The carbon content can be further increased by admixing high carbon gas-house tar with the coke oven tar before distilling it.-

The distillation of coke oven tar at a retort gas plant, where the coke oven tar is available, has the further advantage that the distilling capacity of the retort gases is greatly in excess of that amount of tar contained in the gases employed, so that an amount of coke oven tar can be distilled at a retort gas plant considerably in excess of the total tar which would be produced at such plant. The distillation of the coke oven tar with scrubbing of the retort gases and separationof a greater or less amount of the heavy pitch and carbon carried thereby, results in giving a composite pitch residue higher in carbon content than would otherwise be obtained from the distillation of the coke oven tar in lower carbon coke oven gases.

In referring to the carbon or free carbon contained in tar and pitch, I use these terms in their ordinary meaning to include not only molecular carbon but also those constituents which remain as an insoluble residue when the pitch or tar is digested with benzol or other similar solvent. The so-called free carbon consists to a considerable extent of hydrocarbons of high molecular weight.

The distillation of high carbon gas retort tar according to the present invention, results in less decomposition of the tar than when it is distilled in ordinary externally heated tar stills, and gives an increased oil yield and a pitch of lower carbon content. Improved pitch products, as well as increased oil yields are thus obtainable directly at the gas retort plant, and without the expense and loss incidental to the handling and transportation of gas-house tar when it is transported to a tar distillation plant for distillation.

The tar to be distilled may be raw tar which contains considerable water in which case the tar can be effectively dehydrated as well as distilled according to the present process. The tar can also be preheated before bringing it into direct contact with the hot retort gases in the stand-pipes to promote the distillation. The distillation can also be carried out in stages to produce successive pitch products of progressively higher melting point, or a series of difierent pitch products of different melting points can be produced at the same time by employing diiferent standpipes for distillation. The pitch products produced may be such as are directly salable or they can be blended with other pitch products or with tar to give composite commercial products.

Where part of a retort gas plant is employed for the distillation of tar, according to the present invention, and the remainder of the plant is operated in the ordinary way with separation of tar from the retort gases, the tar collected from the gases in the standpipes or hydraulic mains or both can be subjected to distillation to produce pitch and distillate oils. In such case, the tarry oils recovered in the ordinary condensing system can also be subjected to distillation, or they can be blended with the distillate oils produced by the distillation. The enriched gases from the distillation can be separately cooled to recover the oils therefrom, or these gases can be passed to the usual condensing system and there subjected to cooling and condensation with the gases that have not been employed for distillation, thereby giving composite tarry oils of greatly reduced content of heavy tar and pitch constituents, which may be so regulated in properties as to be directly utilizable, for example, for creosoting purposes as a substitute for so-called coal tar solutions. Where the clean or relatively clean oils from the distillation are separately condensed, they may be condensed fractionally to give heavier, medium and lighter oil fractions, for example, heavier creosote oil fractions, and lighter tar acid oil fractions, etc.

The invention will be further described in connection with the accompanying drawings illustrating an apparatus embodying the invention and adapted for the carrying out of the process of the invention. It is to be understood however, that the drawings are merely illustrative and that the invention is not limited thereto.

In the accompanying drawings:

Fig. 1 is a diagrammatic plan view of a retort gas plant;

Fig. 2 is an elevation of a section of the plant of Fig. 1;

Fig. 3 is an end elevation of a modified form of construction;

Fig. 4 is an end elevation taken at right angles to the view of Fig. 3;

Fig. 5 is a sectional elevation showing one of the insulated standpipes and part of the retort gas plant of Figs. 1 and 2; and

Fig. 6 shows a modification of the standpipe and foul gas main construction.

Referring to the drawings, the furnace structure 5 has a plurality of retorts 6 supported therein so that they are heated by combustion gases. The retorts shown are horizontal retorts.

Multiple standpipes 8 are provided, each connected through connections 7 with a plurality of retorts. In Fig. 2 a tier of four retorts is connected to each standpipe while in Fig. 3 two tiers each of four or more retorts are connected to a single standpipe. The arrangement is such that the gases from one or more tiers of retorts pass into the multiple standpipes and thence to a gas collecting main or foul gas main.

The system illustrated in Fig. 1 is divided into two parts so that each part can be operated independently, or the entire system operated as a unit in either of two ways. The foul gas main 16 has a Valve 31 therein by means of which a section of the main 25 can be disconnected from the remaining portion, and, when so disconnected, the main 25 is connected with two of the standpipes and the main 16 with the remainder of the standpipes. When the valve 31 is opened, the main 16 and the short section 25 form a single foul gas main connected to all of the standpipes of the block. The arrangement is such as to enable all of the standpipes to be employed for the distillation of tar, when this is desired, or to enable only part of the standpipes to be so employed and the remainder to be operated in the ordinary way, or with cooling of the gases in all the standpipes to separate tar therefrom. Likewise, the standpipes on section 25 of the main may be used for distilling one type of tar and those on section 16 for distilling another type of tar. By cl osingvalve 3-1' the gases from-the separate distilling systems may be kept separate and the products of distillation separately collected.

The arrangement is also such that the two standpipes connected to the main 25 can be employed for distillation, and the remaining standpipes connected to the main 16 employed without tar distillation and for cooling of the gases therein to separate tar therefrom, and this operation will be more particularly described.

Each standpipe which is to be employed for tar distillation is provided with one or more nozzles for introducing tar therein. Two nozzles are shown indicated respectively at 10 and 12, sup plied with tar by pipes 11, from a suitable source of tar supply. The nozzle 10 is arranged near the upper end of the standpipes while the nozzle 12 is arranged near the connection of the upper retorts with the standpipes. By using one or a plurality of spray nozzles, a sufiicient amount of tar can be introduced to flush the sides of the standpipes and to bring the tar in finely divided form into contact with the gases rising through the standpipes so as to eiTectively heat the tar and distill it and at the same time scrub the gases from part of their suspended carbon and pitch constituents. The partly distilled tar or pitch collects at the bottom of the standpipes in receptacles 13 which as shown have baflies 14 forming a seal against escape of gas and overflow outlets 15 for maintaining a uniform level. The standpipes are also shown as provided with suitable valves for closing off the individual retort connections when the retorts are being discharged and charged.

The foul gas main 16 is provided with similar spray nozzles connected to pipe 18 for supplying ammonia liquor which is sprayed into the standpipes to cool the gases therein so that tar is con densed and separated therefrom and collected with the excess ammonia liquor in receptacles 13 at the lower end of the standpipes. Outlet pipe 19 is provided for conveying the tar and liquor from these receptacles to a separator 20 where the separtion of tar and liquor takes place, the

tar being collected through pipe 22 in the tar receptacle 21 and the ammonia liquor being collected through the pipe 23 in liquor receptacle 24 from which the liquor is circulated by means of a pump to the supply pipe 18 for the ammonia liquor sprays in the standpipes.

, The tar collected in receptacle 21 can be pumped by pump 26 through line 27 to the line v In the system illustrated, the part of the plant in which ammonia liquor is introduced into the standpipes and which is connected to the foul gas main 16 has a condensing system which may be of any suitable type, and the distillation part of the system connected to the short main section 25 is also provided with a separate condensing system, although in many cases the ordinary condensing system may be used; no separate condensers will in such a case be required.

The foul gas main 16 has its gas main 32 lead- 44 to an exhauster, ammonia saturator, etc. (not shown). The light tar and tarry oils, together with condensed ammonia liquor from the condenser 33 may betaken off through line 39 to separator 40 from which the light tar or tarry oils can be drawn off at 41 and the ammonia liquor pumped by pump 42 through line 43 to the liquor storage and supply tank 24.

The gases resulting from the distillation of tar in the standpipesconnected to the main 25 pass through the gas line 45 to a separate condensing system shown as two condensers 46 and 47 cooled by the direct introduction of a cooling liquid. The condensates are drawn off respectively at 49 and 48 and may be combined in the receiver 50 or kept separate. The gases from the condensers 7 pass through line 51 and may be combined with the gases from the remainder of the plant escaping through line 44 and pass therewith to the exhauster and ammonia saturator, etc.

In the system thus described, ammonia liquor collected in the supply tank 24 is introduced into the standpipes connected to the foul gas main 16 and serves to cool the gases in these standpipes and to flush the surfaces of the pipes so that the greater part of the tar contained in the gases will be collected in the receptacles at the bottom of the standpipes together with ammonia liquor. The ammonia liquor and tar are then separated in the separator .20 and the tar and ammonia liquor respectively collected in the storage tank 21 and 24. The ammonia liquor is recirculated and, additional ammonia liquor supplied from the separator 40 or fresh liquor added in regulated amount and any excess ammonia liquor of high fixed ammonia content drawn ofi as required for the recovery of the ammonia therefrom.

The foul gas main 16 is not operated as a hydraulic main, and any tar or tarry oil condensed therein is permitted to flow back into the standpipes so that the total tar produced is collected either from the bottom of the standpipes or from the condensers.

The standpipes connected to the short main 25 are supplied with tar in the manner above described and the heat of the hot gases is employed for its distillation, while the gases are themselves cooled to some extent, but still maintained at a sufficiently high temperaturejo insure that a large part of the normal vapor content of the gases will be retained in vapor form,

and so that the tar will be effectively distilled and the gases enriched in vapors from the distillation. The partly distilled tar or pitch collected at the bottom of the standpipes can be recirculated for further distillation and to assist in keeping the standpipes flushed to prevent accumulation of hard pitch or carbon therein. The pitch can be recirculated together with regulated amounts of fresh tar and the distillation and flushing of the standpipes thereby regulated. The final pitch product is drawn ofi into pitch receptacl e s 53 through line 54.

The gases collecting in the foul gas main 25 will be hot gases enriched in oil vapors from the distillation. These hot gases pass through the gas line 45 to the condensers 46 and 47 where the distillate oil is condensed. Because of the enrichment of the gases in oil vapors, and the cleaning of the gases in the standpipes to a greater or less extent, the oils collected in the condensers 46v and i? will be relatively clean oils in that they will be much freer of heavy tar and pitch constituents than ordinarily obtained in the condensing system of retort gas plants. They may if desired be returned and subjected to further distillation in the standpipes to free them still fiu'ther from heavy tar and pitch constituents. The light tar or tarry oils from the main condensing system, collected in separator 40, can also be supplied to the standpipes and there subjected to distillation. Tar from another source can be supplied through line 52 and admixed with the retort gas tar so that a composite tar is subjected to distillation and a composite pitch product produced.

In case the entire battery is to be employed for distillation, the supply of ammonia liquor through the pipe 18 is out off, and the valve connecting this pipe with the pipe 11 is opened so that tar can be supplied both through the line 11 and the line 18 to all of the standpipes of the battery. In this case, the separator 20 will serve as a pitch receptacle, or all of the pitch can be collected in the receptacle 28. In this case the valve 31 which separates the foul gas main 16 from the short main 25 is opened or can be opened so that all of the gases from all of the retorts will pass through the foul gas main 16 to the main condensing system of the plant. In this case the separate condensing system is unnecessary although it can be employed if desired.

By keeping the valve 31 in the foul gas main closed and employing the storage tank 24 for supplying tar, two separate tar distillation systems are provided, one connected to the short gas main 25 and with two standpipes, and the other connected with the foul gas main 16 and the remainder of the standpipes. By operating these twosystems independently for the distillation of tar and the production of pitch, two different nection of the pipes 11 and 18 through which the liquor can be supplied to all of the standpipes, and through the common connecting pipes at the bottom of the standpipes through which the tar and liquor from all of the standpipes can be drawn ofi together to the separator 20.

In order to avoid unnecessary loss of heat in the gases entering and passing up through the standpipes, these standpipes are provided with heavy insulation, shown conventionally in Fig. 5. This enables the gases leaving the retorts to be maintained at practically their maximum temperature until they are brought into direct and intimate contact with the tar or pitch flowing down through the standpipes, so that the high temperature and maximum heat of the gases can be effectively employed for distilling the tar. The flushing of the standpipe walls will nevertheless keep the walls free from pitch and carbon accumulations. The pitch or tar flowing down over the inside walls of the standpipes will be exposed to the gases in the form of a film, while the finely divided tar or pitch atomized into the gases will likewise be exposed to the distilling action of the gases and will assist in scrubbing the gases and cooling them to the extent required to condense heavier tar and pitch constituents while leaving the gases sufficiently hot to insure that a large part of the oil vapors will be retained in vapor form in the gases leaving the top of the standpipes. Any condensates forming in the foul gas main '25 will run back into the top of the standpipes. By insulating these foul gas mains, condensation can be reduced to a minimum and the gases passed over in a hot enriched state to the condensers.

The refluxing of such condensate from the foul main will reduce the distillation capacity of the system and will for any given rate of tar feed result in production of softer pitch. If this effect is not desired the connection of the standpipes to the main may be as in Fig. 6, in which case the material condensed in the foul main may be drawn off from the foul main and be combined with the condensate from the condensers or may be held separate as desired. Such condensate will comprise a heavier distillate or tarry oil than that subsequently recovered in the condensers. When the condensate in the foul gas mains does not return to the standpipes, it is drawn oiT through lines 60 and 61 to suitable receptacles (not shown).

In the operation of the apparatus and the carrying out of the process of the. invention, the retorts will be charged with coal to be distilled in the ordinary. way and the distillation will be carried out in the ordinary way. By charging the retorts at different intervals, a constant flow of gases will be obtained in the standpipes. The gases leaving the standpipes at a high temperature will be effectively employed in the standpipes for distillation of the tar or pitch,.and will themselves be cooled by the distillation sufficiently to reduce danger of further decomposition to a minimum, without however, coolingthe gases to a low temperature. The operation of the standpipes is thus improved and objectionable pitch and carbon deposits prevented or reduced to a minimum while the gases are nevertheless employed at a high temperature and in an effective manner for the distillation of tar and the production of pitch and dstillate oils therefrom.

Where the tar available for distillation requires the maximum distillation capacity of the plant, all of the standpipes can be employed for such distillation. In this-way, tars from other plants can be effectively distilled, as where the tar from several plants is available and is distilled at a single retort gas block. Where, however, the tar to be distilled is only that produced at the plant, the greater part of the plant can be operated with ammonia liquor to cool the gases in the standpipes and separate tar therefrom, and the tar so separated either with or without that separated in the condensers, can then be subjected to distillation in a part of the standpipes with utilization of the heat from a part only of the gas retorts.

The pitch produced from retort gas tar of high carbon content will be a high carbon pitch, but it will have a lower carbon content than pitch produced from the same tar distilled in ordinary externally heated tar stills. The carbon content and other characteristics of the pitch may be modified and controlled by adding more or less tar from other sources such as coke oven tar with a lower free carbon content and distilling it in admixture with retort gas tar of higher carbon content. Thus it is possible by the practice of the invention to produce pitches of different kinds suitable for a variety of uses and at the same time to recover valuable oil constituents in a merchantable condition. The oils can be employed, for example, as creosote oils, or for blending with other oils or tars for creosoting purposes.

By subjecting the hot enriched gases, while still at a high temperature, to a further cleaning treatment, as by an electrical precipitator, or a hot pitch scrubber, the gases can be freed completely or substantially so from suspended heavy tar and pitch constituents at a sufficiently high temperature to leave a large part of the oils in the form of vapors so that on subsequent cooling clean oils can be directly recovered therefrom. If the cleaning of the gases is at a sufiiciently high temperature, the total oil recovered can be employed as a creosote oil, or by fractional condensation a creosote oil and a lighter tar acid oil can be produced, and the tar acid oil can be extracted for the recovery of tar acids therefrom.

The pitch products produced by the present invention can also be directly employed for purposes where a high or medium carbon content pitch is required. By proper blending of coke oven tar and retort gas tar and distilling them, a pitch can be directly produced containing, for example, 12 to 15% so-called free carbon and i having a melting point around 105 to 110 F.

which can be employed directly as a road treating tar. Higher melting point tars can also be produced of regulated high carbon content suitable for use for example, for roofing and similar purposes.

In addition to producing pitches of varying melting point either from the retort gas tar or from coke oven tar or from a blend or mixture of different tars, the pitches produced may themselves be blended or out back with raw tar, or

. then blended with raw or dehydrated gas-house tar of high carbon content, or with a gas-house tar which has been only partly distilled to make a relatively low carbon pitch. This will produce a so-called cut-back pitch of lower melting point than that of the pitch before it is blended or out back with the raw tar or lower melting point pitch. Similarly, higher carbon gas-house tar can be disstilled by itself to produce a relatively high melting point pitch, and this pitch can then be cut back with coke oven tar or with lower melting point coke oven pitch. So also, gashouse tar and coke oven tar may be distilled separately to pitches of the same or diiferent melting points and the resulting pitches may be blended to give a composite pitch of the desired melting point and carbon content or composition.

In general, where pitches are to be made from blended tars it will be easier to carry out the process if the tars are blended and the blends distilled or if the coke oven tar is distilled to a hard pitch base and then cut back with the gashouse tar. However, straight gas-house tar pitches can be made by the present process if precautions are taken to circulate sufficient quantities of tar or pitch to avoid accumulations of solid coke or carbonaceous deposits or pitch on the insides of the standpipes. Where such deposits form, they can readily be removed by cleaning in the Well known manner.

Where blended tars are distilled, the distillates produced will also be blended distillates, for exfrom the ordinary process of tar distillation since they contain oils commonly destroyed in the ordinary process of distillation. These oils are present in the products of my process in considerable amount. The total yield of distillate oils produced in distilling up to any particularly melting point pitch by my process is substantially higher than with ordinary distillation processes.

The present invention is of more or less general application to existing retort gas plants having standpipes for leading the gases from the retorts to the gas main, and particularly to plants having multiple standpipes, each connected to a plurality of retorts. In applying the invention to retort gas plants, for example, such as are provided with means for supplying ammonia liquor to the standpipes to cool the gases rapidly therein, the operation is radically changed by avoiding such rapid cooling, and

by insulating the standpipes and keeping the operations in which the gases are rapidly cooled and tar separated therefrom. This high temperature operation is carried out with the avoidance of dissipation of the heat from the gases and the utilization of the heat and high temperature of the gases for the effective distillation of tar and the production of pitch and distillate oils therefrom.

It will be understood that the apparatus as specifically illustrated, and the operation thereof described, can be modified and various changes made therein to adapt all or a part only of the plant for distillation and to permit the distillation of a greater or smaller amount of tar to produce pitch products of varying melting points and compositions and valuable distillate oils. The

invention thus makes possible the working up and distillation, at the retort gas plant, of the tar produced at such plant, and/or of tar produced at other plants, so that only merchantable productsare produced therefrom at the retort H gas plant.

I claim: 1. The method of operating retort gas plants having gas retorts and standpipes for the removal of gases therefrom, and or" distilling tar pipes, and regulating the amount of tar and avoiding the dissipation of heat from the gases to bring about effective distillation of the tar or pitch by the gases, withdrawing the pitch pro-- duced by the distillation from the standpipes,

and Withdrawing the resulting gases and vapors while still at a high temperature from the standpipes and cooling the same to condense oils therefrom.

2. The method of operating retort gas plants having standpipes and retorts for the removal of tar therefrom and for producing pitch and distillate oils therefrom, which comprises bringing the hot coal distillation gases evolved from the retorts into intimate contact with tar or pitch to be distilled and presenting a very large surface area of tar or pitch to direct contact with the gases immediately after the gases leave the retorts, regulating the amount and intimacy of contact of the tar and avoiding the dissipation of heat from the gases to bring about rapid distillation of the tar or pitch by the hot gases, collecting the pitch resulting from the distillation, drawing off the gases and vapors from the distillation while still at a high temperature, cooling the gases and vapors to condense oils therefrom, and recirculating the tar or pitch resulting from the distillation and bringing it into intimate contact with the hot gases in the standpipes to effect further distillation and the production of a pitch of higher melting point and an increased distillation of higher boiling point oils.

3. The method of operating retort gas plants having gas retorts and standpipes for the removal of gases therefrom, and of distilling tar to produce pitch and distillate oils therefrom, which comprises withdrawing the gases from a plurality of gas retorts directly into a common standpipe, preventing loss of heat by providing insulation for the standpipes to maintain the gases therein at a high temperature, introducing into the standpipes the tar or pitch or oils to be distilled and regulating the amount thereof and the intimacy of contact thereof with the hot gases to bring about effective distillation thereof by the gases and to maintain the Walls of the standpipes free from objectionable deposits of hard pitch or carbon, collecting the pitch residue from the distillation, drawing on the gases and oil vapors resulting from the distillation while still at a high temperature and cooling the same to separate oils therefrom.

4. The process according to claim 1 in which the hot gases and vapors escaping from the standpipes are subjected to a further cleaning treatment while still at a high temperature to remove suspended pitch particles therefrom, and in which the resulting cleaned gases and vapors are then cooled to condense clean oils therefrom.

5. The method of operating retort gas plants having gas retorts and standpipes for the removal of gases therefrom, and of distilling tar to produce pitch and distillate oils therefrom, which comprises atomizing or spraying tar to be distilled into the hot coal distillation gases as these gases are evolved from the retorts, avoiding dissipation of heat from the gases, and both regulating the amount of the tar spray and maintaining the fine tar spray in contact with the hot gases for a suflicient time so as to bring about effective distillation of the fine spray of tar to a pitch having a melting point of at least 105 F. by the available heat in the gases.

6. The method of operating retort gas plants having gas retorts and standpipes for the removal of gases therefrom, and of distilling tar to produce pitch and distillate oils therefrom, which comprises combining the gases from different groups of retorts in standpipes, cooling the gases in said standpipes by the introduction of cooling liquids and collecting tar from the cooled gases,

bringing the collected tar into intimate contact with hot gases from other retorts in another standpipe or standpipes, and regulating the introduction of such tar with avoidance of dissipation of heat from the gases to bring about effective distillation of the tar by the gases in the standpipe or standpipes to produce pitch and distillate oils, drawing off the resulting pitch, drawing off the resulting gases and admixed vapors from the distillation and cooling the same to condense oils therefrom.

'7. The method of operating a retort gas plant having horizontal gas retorts and standpipes for removal of gases therefrom, and of distilling tar to produce pitch and distillate oils therefrom, which method comprises introducing a spray of the tar into a standpipe int-o intimate contact with the hot retort gases passing therethrough while the gases are still at a temperature not greatly below that at which they left the horizontal retort and maintaining the tar in the form of spray in contact with the hot gases for a sufiicient period of time so that a large part of the volatile constituents of the tar is distilled off by the hot gases.

8. The method of operating retort gas plants having horizontal gas retorts and standpipes for the removal of gases therefrom, and of distilling tar to produce pitch and distillate oils therefrom, which method comprises passing the gases from a plurality of the gas retorts directly into a standpipe, contacting a spray of the tar with the coal distillation gases in the standpipe while the gases are still at a temperature of about 500 (3., and maintaining the tar in the form of spray in contact with the hot gases for a sufficient period of time so that a large part of the volatile constituents of the tar is distilled off by the hot gases.

9. The method of preparing a composite pitch product of high free-carbon content from coke oven tar at a retort gas plant having horizontal gas retorts and standpipes for the removal of gases therefrom, which method comprises bringing coke oven tar into intimate contact with the hot coal distillation gases passing through a standpipe while the gases are still at a high temperature, and maintaining the tar in intimate contact with the gases in the standpipe for a sufiicient period of time to partially cool the gases and remove pitch constituents therefrom and to distill 01f a large part of the volatile constituents of the tar by the gases, whereby a composite pitch product of high free-carbon content is formed comprising pitch constituents recovered from the retort gases and pitch constituents recovered from coke oven tar.

10. The method of preparing a composite pitch product of high free-carbon content from coke oven tar at a retort gas plant having horizontal gas retorts and standpipes for the removal of gases therefrom, which method comprises spraying coke oven tar into the hot coal distillation gases passing through a standpipe while the gases are still at a high temperature and maintaining the tar in the form of spray in contact with gases in the standpipe for a sufficient period of time so that a large part of the volatile constituents of the tar is distilled off by the gases, whereby pitch constituents are separated from the hot retort gases and the coke oven tar is distilled to pitch and the coke oven tar pitch is blended with the pitch separated from the hot retort gases to form a composite pitch product of high free-carbon content.

STUART PARMELEE MILLER. 

